Failure has become a risk in coaching a big club. There is no coach who has pursued a career without problems. It takes a long process to achieve success. He is still young and needs a lot of experience to become a great coach. If he just stays in his comfort zone, he won't get a lot of good experience. he needs to think about his future, not just stay in one place, I know he has good potential, it's just that his dismissal at Bayern Munich made him step down from coaching in the big leagues.
If he doesn't want to coach a big club which is full of pressure, he can coach a mid-table club in the Bundesliga and improve his performance, who knows, maybe that could increase his value. Slowly start to train mentally and be confident again to be able to coach a big club.
That's a risk too though, I mean think about it you already reached Bayern level before but got fired and if you decide to go to some mid level team and fail there too then you are not going to find any good chances anywhere again, you will drop more and more, basically become like last 5-6 years of Mourinho.
However, he found the biggest job he could, he accepted Germany offer because that was the biggest offer he had, and that means if he does well (which I think he did so far) then he is going to keep being a good manager and could find a job somewhere eventually. This is why I believe that he is doing the right thing, he should keep being there, and eventually the reason they are going to end up being better would be perfect.